Scientific Intelligence. 

 1 give the corresponding specific heats under const 

 Constant Pressure. Constant Volume. 



Carbonic oxide, -2426 



Carbonic acid, '1952 -2169 



-Pogg. Ann., clvii, 1. 

 3. Crooke's Radiometer. — Mr. G. J. Stone 



;rooKes naaiomeier. — Mr. ir. j. stone y presents an expia- 

 of the apparent repulsion produced by heat, according to 

 ine mnetic theory of gases. Mr. Crookes has shown that the 

 pressure produced on a blackened surface of two square inches by 

 the light of a standard candle six inches distant would be -001772 

 grains or somewhat less than -01 milligram per square centimeter. 

 Assuming that the pressure of the air in the interior is reduced to 

 •1 mm. there would still be something like a hundred million of 

 millions of atoms in each cubic millimeter. These atoms will con- 

 sist in part of oxygen and nitrogen from the air, of mercury and 

 hydrocarbons, and probably in part of platinum, glass and other 

 substances in a gaseous form. 



The blackened surface will be heated by the candle more than 

 the glass by an amount which may be assumed at -1° and the air 

 in contact with it will vary in temperature from that of the disk 

 to that of the enclosing air. Were the air at its ordinary pres- 

 sure the heated layer would be very thin, and may be estimated 

 at about -0005 mm., or about the wave-length of green light. 

 With the small pressure here employed, however, the case is quite 

 different, and the thickness of the laver would equal -0005 X 

 (7600)1-3 3, o,, oypj. a decimeter. The heated layer therefore ex- 

 tends to the wall of the surrounding vessel, and now a heat engine 

 is formed by the particles of air which strike the disk with a veloc- 

 ity due to a temperature of perhaps 15°, and are repelled from it 

 with a velocity due to its temperature of 15'1°. The resultant 

 pressure on the disk may be readily computed and is found to be 

 •0115 milligram which agrees closely with -01, as observed by Mr. 

 Crookes. In other words a difference of temperature of -l" C. is 

 sufficient to account for the observed pressure,— PM. Mag., 1, 177. 

 ; here referred to, is described in Engineering, 



[Tl 

 Feb. 18th, and was effected in the following manner : A torsion 

 balance was constructed wdth a horizontal glass fiber and with a 

 horizontal arm terminating in a cup at one end and in a disk of 

 pith at the other. A small piece of iron weighing a hundredth 

 of a grain was raised by a magnet and dropped into the cup. ^ It 

 was then found that the fiber must be turned through 100021 to 

 bring the arm back to its original position. The light of a candle 

 at a distance of 6 inches w^as next allowed to fall on the pith, when 

 a torsion of 1775'* was required to bring it back. This corres- 



